This application is a 35 USC 371 filing based upon PCT/DE98/01918 filed Jul. 09, 1998.
The invention relates to a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engines, particularly in a common rail injection system, with a drive shaft that is supported in a pump housing and is embodied as eccentric or has a number of cam-like projections in the circumference direction. The pump includes a number of pistons that are disposed radially with regard to the drive shaft, each in a respective cylinder chamber, and can be set into a reciprocating motion in the radial direction in the cylinder chamber upon rotation of the drive shaft. Each respective cylinder chamber is sealed on the radial outside with regard to the drive shaft by a valve plate that has an intake side check valve and a high-pressure side check valve.
A radial piston pump of this kind has been disclosed by DE 44 01 074 A1. The check valve is provided on a side of the valve plate oriented toward the cylinder chamber, in a diametrically enlarged section of the cylinder chamber. A valve body that can be placed against a sealing seat of the valve plate or can be lifted up from the sealing seat is contained in a basket- or cup-shaped component which extends into the cylinder chamber toward the respective piston and is fastened to the valve plate.
The valve body is pressed toward the valve plate by way of a disk spring provided at the bottom of the cup-shaped component.
Based on this known radial piston pump, an object of the current invention is to improve its efficiency.
In a radial piston pump of the type mentioned above, this object is attained according to the invention by virtue of the fact that the intake side check valve has a tappet that passes through the valve plate and this tappet, on its end oriented toward the cylinder chamber, has a valve disk that can be placed in a sealed fashion against a sealing seat of the valve plate. On a side of the valve plate remote from the cylinder chamber, a device is provided which pre-stresses the tappet in the closing direction.
In this manner, the dead space that defines the piston stroke, i.e. the structural space of the intake side check valve, is significantly reduced. In the known radial piston pump, the stroke of the pump piston was defined by the outside of the cup-shaped component. Now, during the compression phase, the piston can extend at least almost to the outside of the valve disk of the check valve, i.e. even into the stroke region of the valve disk of the check valve. The dead volume is thus minimal and the efficiency of the radial piston pump is greater than in the previously known pump.
In a preferred embodiment of the radial piston pump according to the invention, the device that pre-stresses the tappet in the closing direction includes a spring, which is supported on one end against the side of the valve plate remote from the cylinder chamber and is supported on the other end against a counter support provided on the tappet.
The disposition of the device, which pre-stresses the tappet in the closing direction, on the side of the valve plate remote from the cylinder chamber brings with it the advantage that the device can be embodied in an intrinsically arbitrary manner so that it supplies a desired opening pressure for the check valve.
The counter support for the spring can be realized in an intrinsically arbitrary manner; for example, an axial stop can be provided on the tappet, e.g. by means of upsetting or notching. In a preferable manner and according to a variant of the invention, the counter support is constituted by a collared bushing element whose bushing section concentrically encompasses the tappet and whose collar section supports the spring. This opens up the possibility of sliding the counter support onto the tappet and fixing it in the desired location.
The fixing of the counter support can take place in an intrinsically arbitrary manner. However, it has turned out to be advantageous if the counter support is attached to the tappet in a positively engaging manner, particularly by means of a crimping work cycle.
In order to preset the opening pressure of the check valve, a spring can be chosen that has particular dimensions or a particular spring constant. However, in order to be able to flexibly preset the opening pressure in the manufacture of radial piston pumps without having to resort to a multitude of various valve springs, which have to be kept on hand for this purpose, the proposal is made to fix the counter support in a position on the tappet such that the desired opening pressure of the check valve is produced. In particular, a counter support in the form of the above-mentioned collar bushing element has turned out to be advantageous for this purpose.
However, it can also turn out to be advantageous if the counter support is constituted by a disk- or plate-shaped component that rests against an axial stop on the tappet, for example a slit securing disk or the like that can be snapped onto the tappet. In such a case, axial stops can be provided at various axial positions on the tappet. However, it may turn out to be more advantageous to provide an axial stop, for example in the form of a circumferentially extending annular groove, and to keep securing disks of various thicknesses on hand and to use them depending on the opening pressure required. The thickness of a securing disk can be determined easily, and the selection during the assembly of the check valve is therefore easy.
In order to be able to optimally employ the structural space on the side of the valve plate remote from the cylinder chamber, it has turned out to be advantageous if at least one opening that is essentially radial to the longitudinal direction of the cylinder chamber is provided in the valve plate and communicates with a fuel supply opening in the housing. According to this concept of the invention, the fuel supply therefore does not occur from the radial outside with regard to the drive shaft, but rather fuel is supplied by way of an opening that extends in the plane of the valve plate. This radial opening then preferably feeds into the tappet through opening of the valve plate.
Other features, details, and advantages of the invention ensue from the graphic depiction and subsequent description of preferred embodiments of the invention.